TUBERCLE BACILLUS 443 



tubercle bacillus usually causes only local lesions, which in the vast 

 majority of instances are not fatal and clear up after some weeks. 

 Massive doses, however, usually produce lesions. Intravenous injec- 

 tion, unless massive doses are given, also fails to kill rabbits as a rule. 

 Occasionally, however, a generalized tuberculosis with fatal termina- 

 tion results. Intraperitoneal inoculations only occasionally bring 

 about a generalized fatal tuberculosis. Usually slight lesions are pro- 

 duced which clear up spontaneously. Ingestion of human organisms 

 rarely leads to infection. 1 



Guinea-pigs. Guinea-pigs are very susceptible to infection with 

 either the human or bovine tubercle bacilli, although the disease 

 rarely appears spontaneously. Theobald Smith 2 has shown that it 

 requires but one fifteen-hundredth as much tuberculous material to 

 infect a guinea-pig as is required to infect artificial media. This 

 susceptibility of the guinea-pig to inoculation with the tubercle bacil- 

 lus explains the well-attested fact that inoculation of suspected tuber- 

 culous material into these animals is a far more delicate test for their 

 presence than attempts to grow the organisms from the same material 

 on artificial media. It must be remembered in this connection that 

 even dead tubercle bacilli stimulate tubercle formation in guinea-pigs, 3 

 hence for an absolutely safe diagnosis whatever tubercles are pro- 

 duced in the first guinea-pig must be ground up and injected into a 

 second guinea-pig. If viable tubercle bacilli are present a successful 

 infection will take place, otherwise the experiment is negative. 



Subcutaneous Inoculation. After ten to fourteen days a small hard 

 nodule appears at the site of inoculation, and very soon afterward the 

 regional lymph glands begin to enlarge and the animal begins to lose 

 weight. The animal usually dies in from two to four months. Post- 

 mortem, the spleen is enlarged, yellowish-brown in color, and studded 

 with tubercles, some minute and gray, others larger, yellowish and 

 frequently caseous. The regional lymph nodes also have usually 

 undergone caseation, particularly the inguinal glands, less com- 

 monly the axillary glands. The liver usually has a few rather large 

 caseous or fibrinous tubercles, particularly on the free border. The 

 kidneys also may have a few tubercles. If the animal has lived two 

 or three months the thoracic cavity is also invaded, and scattered 

 miliary tubercles may be seen on the lungs. The mesenteric, bronchial, 

 sternal and cervical glands are invaded. 



1 Theobald Smith, Jour. Med. Research, 1905, xiii, 253. 



2 Jour. Med. Research, 1913, xxviii, 91. 



3 Prudden and Hodenpyl, New York Med. Jour., 1901, and others. 



